In the latter half of 1960's, a linear accelerator (hereinafter referred to as "linac") appeared as means for treating cancer. Because of its simple acceleration principle and enhanced reliability on its microwave source, it gained a high evaluation as practical radiotherapeutic apparatus and rapidly came into use. Then, with the development of various high-energy radiotherapies, great importance has come to be placed on highly accurate therapeutic planning. The overall process of a radiotherapy includes the following stages. The first is the stage of diagnosis, that is, to correctly detect position, size, shape, etc. of the diseased part by utilizing, for example, X-ray CT images. The second is the stage of making up a therapeutic plan, that is, to decide the kind of curing radiation, the dose, the direction of irradiation, the area to be irradiated, etc., on the basis of various data obtained at the time of diagnosis. The third is the stage of execution of the medical treatment, that is, to position the area of irradiation on the body of a person being examined, confirm it, and apply the radiation thereto. The fourth is the stage of management, that is, collation, recording, retention, etc. of data obtained in the stages of diagnosis, planning, and execution of medical treatment.
In order to define the area of irradiation for radiotherapy, tomographic images obtained by an X-ray CT etc. and a perspective image obtained by an X-ray simulator have so far been utilized. The interior of the body being examined can be shown with high contrast and resolution in the tomographic image by means of the X-ray CT, the diseased part (region of interest) can be specified in the tomographic image relatively easily. In the perspective image by means of the X-ray simulator, the visual point for perspective viewing is set in concurrence with the center of radiation of the curing radiation. Therefore, the region of interest in the perspective image can be easily brought into concurrence with the relative part on the surface of the body being examined. At the time of execution of the radiotherapy, the body being examined is moved onto the table of the therapeutic apparatus, the perspective image obtained by means of the X-ray simulator on a film is projected with light on the surface of the body being examined, the region of diseased part to be treated is drawn on the body being examined by tracing the projected image with a felt-tip pen or the like, and then the collimator aperture at the radiation emitting window is adjusted to the region of the diseased part drawn on the body being examined, and thereafter, the radiation from the radiation source is applied to the body being examined.
Since, as described above, tomograms are taken with an X-ray CT, the body being examined is then moved into an X-ray simulator to have a photograph of perspective image taken, the body being examined is then moved onto the table of a therapeutic apparatus to have the perspective image in a film projected on the surface of the body being examined so that the region of diseased part to be treated is marked with a felt-tip pen by tracing the projected image, that is, various operations are performed by the use of separate apparatuses, much labor and time have so far been taken. Further, many operations, such as the setting of the film of the perspective image on the therapeutic apparatus and the setting of the collimator of the therapeutic apparatus, have relied on manual work of the operator. Therefor, much time and labor have been required for such operations and this has been the cause of personal mistakes.